Question

Sum of 21 consecutive term of an arithmetic sequence is 420. What will be the 11 term

Answer 1

Answer:

20

Step-by-step explanation:

Given: S₂₁ = 420

Sₙ = n/2( 2a + (n-1)d)

S₂₁ = 21/2( 2a + 20d)

420 * 2/21 = 2(a +10d)

40 = 2 (a+10d)

40/2  = a+10d

20 = a+10d (1 eq.)

aₙ= a + (n-1)d

so 11 th term is:

a₁₁ = a + 10d

[puuting 1st eq.]

a₁₁= 20